In keeping with the mission of NIDDK to support research to combat the many debilitating and costly chronic diseases, including diseases of the liver, and in particular the ?identification of biomarkers that can aid in the diagnosis of disease and in the assessment of new treatments?, the overarching goal of this proposal is to develop novel metabolic imaging biomarkers for the improved diagnosis and treatment monitoring of nonalcoholic steatohepatitis (NASH). Nonalcoholic fatty liver disease (NAFLD) is emerging rapidly as the most common form of chronic liver disease in the world and prevalence in the US is believed to be 20-46% Approximately 20% of NAFLD patients will progress to the much more clinically deleterious NASH, which in turn can lead to cirrhosis, liver failure, and hepatocellular carcinoma. Fueled by the current epidemic of obesity and type 2 diabetes mellitus, the diagnosis and treatment of NASH and associated liver pathologies has emerged as a major clinical challenge. The diagnosis of NAFLD is typically made using a combination of ultrasonography and blood tests. However, definitive diagnosis of NASH can only be obtained through liver biopsy, an invasive procedure, which poses its own risks and is also subject to sampling errors. Presently, there are no non-invasive biomarkers to differentiate the critical stages of disease progression in NAFLD, and in particular for discriminating NASH from the earlier stage of benign fatty liver (steatosis). The critical distinction between NAFLD and NASH is the presence of inflammation that is only a feature of the latter ? and which 13C magnetic resonance (MR) spectroscopy is ideally suited to detect in a non-invasive manner. The recent development of hyperpolarized 13C MR spectroscopy enables for the first time the real-time non-invasive measurement of critical dynamic metabolic processes in vivo. Here, we propose to advance a set of hyperpolarized 13C metabolic imaging tools optimized for noninvasive diagnosis and staging of NAFDL/NASH and conduct a series of studies to validate these proposed biomarkers. Specifically, we will develop optimized MR acquisition techniques combined with kinetic modeling tools for the improved measurement of apparent maximum reaction velocities as quantitative markers of alanine aminotransferase activity, inflammation, and necrosis in vivo (Aim 1) and evaluate the biomarkers in a dietary rat model of NASH that mirrors the disease progression in humans (Aim 2). Finally, in Aim 3 we will develop the imaging tools necessary to translate this methodology to human subjects. The successful completion of these goals will provide for the first time quantitative biomarkers for the direct, noninvasive monitoring and staging of liver disease with a clear translational path of this technology for the assessment of NASH in patients.